The PTB at the 1997 Hannover Fair

50 years ago, on the initiative of the British military government, the first fair in Hannover opened its doors. In the ensuing decades, the HANNOVER FAIR developed into the world economic summit and now as before is considered a barometer of the economic situation.

Close connections developed in the course of history make Great Britain this year's partner country of the HANNOVER FAIR. Its economy will present itself with the slogan "British Excellence".

In the 25 halls and in the open-air grounds, more than 7100 exhibitors from 69 countries participating in this jubilee fair will present on an international scale industrial techniques in the following main focal areas: automation technology, motive power engineering and fluid technology, production engineering, lighting engineering, ancillary supplies, materials, pneumatic techniques, operating techniques and tools, railway traffic engineering as well as research and technology.

On the innovations market "Research and Technology" in Hall 18, about 600 exhibitors from more than 20 countries will again practice international technology transfer, scientists offering to practicians from the economic sector products and procedures fully developed and suitable for application.

Within the scope of this innovations market, the PTB will again be present as an exhibitor. At the PTB stand, members of the PTB staff will provide information about the tasks and organization of the PTB and the Deutscher Kalibrierdienst (DKD, German Calibration Service), reply to questions concerning accreditations, the mutual recognition of calibrations, tests and certifications etc., and be available for discussions about technical problems arising in the calibration of measuring and testing equipment.

Brochures and graphs available at the stand will inform about current tasks of PTB, as will exhibits which will be shown as examples of the latest results of research work concerning the following subjects:

High-capacity laser Doppler velocimeter for complex flow processes

Laser Doppler velocimeters are well suited for non-interacting metrological investigations of fluid flow phenomena. The interest in improved facilities for the investigation of extremely slow flow processes is steadily increasing, for example in environmental and medical measuring techniques. Here it is above all the determination of flow processes with extreme velocity variations and inversion of the direction of flow, which places high demands on the LDA systems.

The PTB presents an efficient sensor concept intended for the velocity measurement in transparent media and/or on light-scattering objects. The sensor excels by a wide measuring range which begins at zero and allows both the value and the sign of the velocities to be measured. The sensor is based on a laser Doppler velocimeter operating according to the Doppler difference method and equipped with two high-capacity 100 mW DBR laser diodes whose optical frequency is made use of for heterodyne and quadrature signal processing techniques.

As the laser power has been doubled, this sensor concept allows smallest scattering particles to be used in the measurement volume. Furthermore, the use of heterodyne and quadrature signal processing techniques makes it possible to identify the direction in velocity measurements, to extend the range of velocity measurements and to carry out measurements of the velocity in the measurement volume with high-sensitivity resolution.

Direct determination of the density on weights of up to 50 kg

Weights must meet requirements not only with regard to the mass or the conventional mass, magnetic susceptibility and surface quality, but also regarding the density: rho = (8000 +- 66) kg/m³ in the highest class E1.

To allow the density to be directly determined also on the heaviest weights for which accuracy classes have been defined by OIML, a density measuring system for weights up to 50 kg has been set up. The density is not determined by the classical hydrostatic procedure using a weighing system for below-balance weighing but by a modern hydrostatic method which is easier to apply and which uses a top-loading weighing instrument. This weighing instrument carries a glass container filled with a liquid into which the suspension mechanism is immersed now in the empty state and now together with the weight.

As has been shown by series of measurements and comparisons with other density measurements, despite wetting of the 50 kg weights, the uncertainties of measurement are less than U(rho) = 2 kg/m³ (P = 95%). This uncertainty influences the determination of the mass of weights with a relative uncertainty of rho a · U(rho)/rho² = 4 · 10^-8 (2), which - unlike the relative error limit for E1 weights of 5 · 10^-7 - can be neglected.

CHEMSAFE

CHEMSAFE is a database for safety data for the field of fire and explosion protection. The database covers data which were evaluated by experts, including recommendations made by these experts. Experts of BAM (Federal Institute for Materials Research and Testing, Berlin) are responsible for the area of dusts and gases, while the PTB is concerned with the characteristic data for flammable liquids. Not only data from the literature are collected, evaluated and stored in CHEMSAFE, but also data determined in the PTB and BAM laboratories. At present, CHEMSAFE contains the data of about 2000 substances: flammable liquids, gases and dusts. CHEMSAFE is updated every year, the increase being about 60 new substances and 1000 data sets per year. CHEMSAFE can be polled online through the STN International data base supplier. In-house versions are available for various computer operating systems. The version for MS Windows PCs will be demonstrated at the Fair. Device for the highly precise measurement of temperatures and other environmental parameters, for example for the field of high-resolution measuring techniques

The temperature measuring device was specially developed for industrial metrology, for example for use in high-resolution dimensional metrology. All functions and specifications required for this purpose have been combined and a solution has been found which meets the requirements of practical applications and is at the same time economical.

The device makes available a number of measuring channels (up to 64) which can be selected at will. Several novel solutions (e.g. zero current correction) allow the high accuracy requirements to be met. The uncertainty of measurement of the electronic system (without sensor) is < 0.3 mK.

To allow optimum performance of the respective measurement tasks, the device can be operated with different temperature sensors distributed and arranged at will. For example, for absolute temperature measurements and simultaneous calibration, a combination of Pt100 and Pt25 sensors (linked up with the ITS-90) can be used. Thermocouples or thermistors can be added for the highly precise measurement of temperature differences. Moreover, in order to measure the refractive index of the air, the device can be supplemented by components which allow the atmospheric pressure, the humidity and the CO₂ content of the air to be measured.

The measuring device is operated with a ROM-resident program of a single-board computer which is controlled via an RS-232 interface. All measuring channels can be separately interrogated through this interface. The measurement values furnished by the sensors can be corrected and converted on the basis of several calibration functions. The calibration functions selected and the calibration values are input through the RS-232 and stored in an EPROM independent of the power system.